Hyperoxia retards growth and induces apoptosis and loss of glands and blood vessels in DMBA-induced rat mammary tumors

Anette Raa,Rolf K Reed,Vidar M Steen,Linda Eb Stuhr,Rolf Bjerkvig,Christine Stansberg

doi:10.1186/1471-2407-7-23

Abstract

BackgroundThis study investigated the effects of hyperoxic treatment on growth, angiogenesis, apoptosis, general morphology and gene expression in DMBA-induced rat mammary tumors.MethodsOne group of animals was exposed to normobaric hyperoxia (1 bar, pO2 = 1.0 bar) and another group was exposed to hyperbaric hyperoxia (1.5 bar, pO2 = 1.5 bar). A third group was treated with the commonly used chemotherapeutic drug 5- Fluorouracil (5-FU), whereas animals housed under normal atmosphere (1 bar, pO2 = 0.2 bar) served as controls. All treatments were performed on day 1, 4, 7 and 10 for 90 min. Tumor growth was calculated from caliper measurements. Biological effects of the treatment, was determined by assessment of vascular morphology (immunostaining for von Willebrandt factor) and apoptosis (TUNEL staining). Detailed gene expression profiles were obtained and verified by quantitative rtPCR.ResultsTumor growth was significantly reduced (~57–66 %) after hyperoxic treatment compared to control and even more than 5-FU (~36 %). Light microscopic observations of the tumor tissue showed large empty spaces within the tissue after hyperoxic treatment, probably due to loss of glands as indicated by a strong down-regulation of glandular secretory proteins. A significant reduction in mean vascular density (30–50%) was found after hyperoxic treatment. Furthermore, increased apoptosis (18–21%) was found after hyperoxic treatment.ConclusionThus, by increasing the pO2 in mammary tumor tissue using normobaric and moderate hyperbaric oxygen therapy, a significant retardation in tumor growth is achieved, by loss of glands, reduction in vascular density and enhanced cell death. Hyperbaric oxygen should therefore be further evaluated as a tumor treatment.

Highlights

This study investigated the effects of hyperoxic treatment on growth, angiogenesis, apoptosis, general morphology and gene expression in DMBA-induced rat mammary tumors
In a rat model of dimethyl-α-benz-anthracene (DMBA)-induced mammary adenocarcinomas, we have recently demonstrated a significant decrease in mammary tumor size after repeated Hyperbaric oxygen treatment (HBO) treatment at 2 bar for 90 minutes [14]
Hyperoxia induces apoptosis We found the amount of normal cells in the tumor to be decreased after hyperoxic treatment

Summary

Introduction

This study investigated the effects of hyperoxic treatment on growth, angiogenesis, apoptosis, general morphology and gene expression in DMBA-induced rat mammary tumors. Growth of solid tumors depends on adequate supply of oxygen and nutrients. There is typically a hypoxic milieu due to structural and functional vessel disturbances (perfusion- and diffusion-limited O2 delivery), while in the periphery there is generally a denser vascular network with subsequent improved blood flow. While normal tissue can compensate for such an O2 deficiency by raising the blood flow, large tumor areas cannot adequately counteract the restriction in O2 supply and develop hypoxia. It is widely accepted that hypoxia promotes tumor growth, angiogenesis and reduce the effect of chemo- and radiation- therapy [3,4,5,6]. We might expect that an increase in the oxygen-content in tumor tissue might have the opposite effect

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